1. Field of the Invention
Methods and Apparatuses consistent with the present invention relate to enhancing contrast, and more particularly to adaptively enhancing contrast for an input image, so that it is possible to prevent unnatural images, due to excessive enhancement of contrast, from being outputted.
2. Description of the Related Art
With the development of a digital electronics engineering technology, conventional analog data has been digitized. Accordingly, digital image signal processing technologies for digitizing and processing image signals have emerged. According to these digital image signal processing technologies, image information is compressed to increase the storage and transmission efficiency of the image information, and more vivid images are provided as compared with the input images, so that various levels of image processing can be accomplished. Among these technologies, a technology for enhancing the contrast of an image has also been actively researched.
According to the prior art for enhancing the contrast of an image, a luminance histogram equalization technique is known. The luminance histogram equalization technique is a method of enhancing the contrast of an input image by analyzing the luminance histogram of the input image and equalizing the distribution of the luminance histogram. Herein, the luminance histogram is the distribution of the luminance of pixels within the image. That is, the luminance histogram expresses the range and values of bright spots and dark spots existing in an image.
However, according to the conventional luminance histogram equalization technique as described above, since only an algorithm dependent on the luminance histogram of an input image is used, contrast may be excessively enhanced. Therefore, the output image may have unnaturally high contrast.
There exists a contrast enhancement method for computing the average and standard deviation of an input image, computing the average and standard deviation of a target image based on the computation results, and then generating a mapping function. However, since such a contrast enhancement method must modify a large quantity of parameters, a relatively high number of operations and amount of processing speed are required.